The present invention relates to engine oil condition, and more particularly to an algorithm for producing an oil condition trend by which the necessity of an oil change may be determined.
An engine oil""s usable life may vary considerably, depending on many factors, such as oil quality, engine type and condition, ambient conditions, and vehicle service schedule. Currently, automobile manufacturers recommend oil change intervals for gasoline engine powered cars and light-duty trucks of either 3 months/3000 miles or 12 months/7500 miles, depending primarily on the vehicle driving cycle and ambient conditions. The use of the proper quality (i.e., SG/CD) engine oil is assumed in recommending these intervals. Several problems exist with the current method of specifying oil change intervals:
(1) The vehicle""s Owner""s Manual may not be read.
(2) Most drivers do not fit neatly into either of the two discrete intervals recommended. Many drivers should probably change oil somewhere between 3months/3000 miles and 12 months/7500 miles.
(3) Most drivers do not keep track of dates of oil changes.
(4) Most drivers do not keep track of mileage between oil changes.
A variety of oil condition sensor systems are known whose output voltage is related to oil conductivity. Systems, utilizing such oil condition sensors, employ computer algorithms to decide when an oil change is necessitated, assuming xe2x80x9cnormalxe2x80x9d engine function and the proper quality and amount of oil in the reservoir. These systems calculate effective oil life by developing an oil condition trend (OCT), based on oil temperature and conductivity verses miles driven or engine-on time, from which an oil change trigger point is determined. The conventional method for developing an oil condition trend specifies that the average of all conductivity points between a fixed temperature range (i.e. 80xc2x0 C. xc2x11xc2x0 C.), when the engine oil is heated up, should be part of the OCT. There are three issues or risks associated with this methodology:
(1) OCT points are calculated during engine operation. Due to the oil condition sensor""s inherent thermal lag, varying engine operating conditions can cause significant errors in the OCT due to sudden temperature variations while the engine is running. These false points create unwanted fluctuation or noise in the OCT, thus reducing the accuracy of the change oil trigger points.
(2) In some applications, OCT points are measured only at a specified temperature. If the engine""s operating conditions are not meeting this particular temperature frequently enough, the accuracy of the OCT suffers or a condition without any OCT at all could occur as a worst case.
(3) The times between the OCT points can vary significantly.
FIG. 1 depicts the conventional methodology of generating a typical engine heat-up (engine-on) OCT for a temperature point of 80xc2x0 C. of a vehicle engine filled with the proper amount of Sunoco 5W-30 oil. The axis 10 represents accumulated engine-on time (in hours) under xe2x80x9cnormalxe2x80x9d driving conditions whereas the axis 12 represents an oil conductivity signal (OCS) (i.e. an oil condition sensor output (in volts)). The first OCT point 14 is defined at an OCS when engine oil temperature reaches 80xc2x0 C. while the engine is running (i.e. on). Subsequent OCT points 16 are defined in a similar manner before which engine oil temperature has cooled below 80xc2x0 C. during engine-off periods (cool down cycles). As can be seen in FIG. 1, the OCT is not time normalized, whereby the time between OCT points can vary significantly, and there are, also, a number of false points (i.e., noise) which can lead to a substantial error in the OCT profile.
Accordingly, what is needed is a more robust method of generating an OCT wherein the previously mentioned issues are addressed.
The present invention is an algorithm by which a time normalized OCT is developed without the shortcomings of the conventional method. During engine off periods, while the engine is cooling, the vehicle""s main computer program implements the trend algorithm according to the present invention by which engine oil conductivity (oil sensor output voltage) and temperature data are obtained in a specified temperature range (i.e. 80xc2x0 C. to 50xc2x0 C.).
The acquisition of these data while the engine is cooling eliminates the false points of the conventional method. This requires that the oil condition sensor distinguish between engine-on and engine-off conditions. It then needs to be able to take measurements after the ignition is turned off. This requires a power connection independent from the ignition switch (battery power). The sensor could then be powered for a certain time after the ignition is off, for example, two hours, to take continuous measurements of oil conductivity data over oil temperature. To save battery power, the sensor could also be switched on and off at certain intervals to take a sufficient number of readings. This condition could be called xe2x80x9csleep modexe2x80x9d in which the sensor xe2x80x9cwakes upxe2x80x9d at certain time intervals to take readings. The means to accomplish the above is well known in the art.
These acquired data are then input into a second order polynomial equation (the cool down equation) to determine its coefficients using nonlinear regression (i.e. least squares fit). This cool down equation models oil conductivity as a function of temperature and is used at a specified time during an engine-on period to calculate an OCT point. Data from subsequent proper engine-off periods generate different values for the coefficients, since oil conductivity changes with time and use, thereby resulting in different values for the coefficients of each calculated OCT point during subsequent engine-on periods. Collectively, these OCT points determine the oil condition trend that is analyzed by a procedure called from the vehicle""s main computer program to determine when an oil change is necessary.
An example of an oil sensor system is described in U.S. Pat. No. 5,274,335, issued on Dec. 28, 1993 to Wang et al, the disclosure of which is hereby incorporated herein by reference.
Accordingly, it is an object of the present invention to develop a time normalized OCT without the shortcomings of the conventional method to determine when an oil change is necessary.
This, and additional objects, advantages, features, and benefits of the present invention will become apparent from the following specification.